A key issue in evaluating the utility of nanomaterials is assessing their potential toxicity- either due to their inherent chemical composition (e.g. heavy metals) or as a consequence of their nanoscale properties (e.g. inhalation of particulate carbon nanotubes). The Toxicity Core (TC) proposed here will therefore provide the Harvard/MIT CCNE investigators the ability to rapidly characterize the potential toxicity of novel nanotechnology formulations using a panel of in vitro and in vivo assays. The Toxicity Core will be directed by Dr. Sangeeta Bhatia (MIT/BWH) in collaboration with the Mouse Model Core and consultants, Dr Jennifer Allport-Anderson (Novartis) and Dr. Monty Krieger (MIT). Models of basal and tissue-specific toxicity (endothelial, liver, and macrophage) will be available to test approximately 100 formulations per year in vitro, and a subset of these will be tested in mice with the input of veterinary pathologist, Dr. Rod Bronson. Promising formulations will be subsequently submitted to the NCL for full characterization through the formal application process or independently characterized by Charles River Laboratories.